LotaMath

Partially due to the increased usage of calculators mental maths skills seems to be in decline, but you can change that with LotaMath. Equally suitable for all ages it supports 7 difficulty levels that range from easy to ultra hard, and you can choose to have addition, subtraction, multiplication, division, a mixture of all or squares. You easily can see how you're progressing as scores are tracked for unlimited different users via a built in database, and there is an overall rating displayed. Various options are supported such as user notes and auto advance.

Limitations:

30-day trial